Aircraft applicable current imbalance detection and circuit interrupter and packaging thereof

ABSTRACT

The aircraft applicable current imbalance detection and circuit interrupter interrupts an electrical circuit when a current imbalance is sensed. The current imbalance detection and circuit interrupter includes a housing, power supplies, a sensor for sensing a current imbalance at the line side of the electrical circuit, a logic controller and a power controller. In a preferred embodiment, the invention can also include a fault indicator, a press to test switch and a reset switch. The power supplies provide power to the sensor, logic controller, and the power controller. The logic controller receives input from the sensor and the relay control signal, and the power controller receives input from the logic controller, and interrupts power to the load side of the electrical circuit when the sensor senses a current imbalance. Power interruption due to a sensed current imbalance is maintained until the line side power source is cycled. The circuit interrupter is preferably autonomous, requiring no additional signals, inputs, wiring or sources of power. The current imbalance detection and circuit interrupter is packaged in a configuration integral with the power controller, thus easing retrofit with the improved aircraft applicable current imbalance detection and circuit interrupter.

RELATED APPLICATIONS

This is a divisional of Ser. No. 09/954,474, filed Sept. 14, 2001, now U.S. Pat. No. 6,618,229 which is a continuation in part of Ser. No. 09/775,337, filed Feb. 1, 2001, now U.S. pat. No. 6,583,975.

BACKGROUND OF THE INVENTION

This invention relates generally to electrical control systems, and more specifically to an aircraft electrical control system which disconnects power to a load when a current imbalance is sensed.

In the elector-mechanical arts, current imbalances are indicative of serious problems that can lead to disastrous results, such as arcing within fuel pumps. Since fuel pumps are often housed within a fuel vessel to directly pump fuel out of the vessel, arcing within a fuel pump can lead to an explosion of fuel-air mixture and a subsequent breach of the fuel vessel, which can be catastrophic. In light of the seriousness of such an event, a device or methodology is needed which can suppress this type of arcing, as well as other associated problems. Presently, a common type of circuit protection device being utilized in aircraft is a thermal circuit breaker. However, arcing typically does not cause thermal circuit breakers to activate. Thus, there has been a long-felt need for the function of current imbalance detection in an aircraft. One very important form of current imbalance is a ground fault in which current is flowing between a circuit or electrical device to ground, when such current flow is not desired. In the prior art, ground fault detection has been addressed by a separate ground fault interruption unit. However, such prior art systems have had limitations, including the necessity of rewiring the aircraft. In addition to the requirement to rewire the aircraft, additional space had to be found to accommodate the ground fault interruption system.

One currently available ground fault interruption unit made by Autronics (model 2326-1) has been used in large commercial aircraft for the purpose of ground fault protection for fuel pumps. The Autronics unit detects a ground fault and outputs a signal indicative of a fault by use of a current transformer and acts by removing power to the fuel pump control relay.

There exists a need for an improved circuit protection device for aircraft. It would further be desirable for the circuit protection device to be included within an existing device in the aircraft, or to be packaged with an existing device, sharing the same connections to existing electrical circuits, since space for avionics is limited in any aircraft and adding wiring to accommodate a new device is very difficult. The present invention addresses these and other concerns.

SUMMARY OF THE INVENTION

Prior art systems for ground fault detection are helpful to reduce arcing in aircraft electrical systems, including aircraft fuel pumps. This issue has become a major concern of the Federal Aviation Administration and recent studies have promulgated a variety of studies and regulations in an attempt to prevent fuel tank ignition. One recent conference on fuel tank ignition prevention hosted by the FAA on the 20^(th) and 21^(st) of June 2001 at the SEATAC Airport Hilton was given in order to better understand the provisions SFAR No. 88 and related certification procedures and airworthiness standards for transport category aircraft. A copy of the materials handed out and discussed at that meeting is attached hereto as Appendix A and incorporated herein by reference. Also attached as Appendix B is a copy of the Federal Register of Monday, May 7, 2001 relating to SFAR No. 88, “Fuel Tank System Fault Tolerance Evaluation Requirements and Related Airworthiness and Certification Standard”. These materials and this conference emphasized the importance of detecting ground faults and operating on the circuit to prevent, to the largest extent possible, arcing within fuel pumps and the like that may be exposed to flammable materials.

In addition to the Autronics Corporation Model No. 2326-1 series ground fault current detector previously discussed (and attached hereto as Appendix C), there also exists a ground fault detection system sold by PRIMEX Aerospace Company as Part No. 437, 437. A brochure for the PRIMEX system is attached as Appendix D. The PRIMEX system uses a current transformer to detect ground fault currents in three phase 400 Hertz motors. However, these prior art systems has serious limitations if they are to be broadly applied to aircraft, either as original equipment or retrofit, and they require separate wiring and space in addition to the currently existing equipment. The present invention offers many operational and functional advantages, in that it fits into the space available on the panel for the existing relays, utilizes the power of the system it is monitoring to operate, and is functionally faster and more efficient in detecting a ground fault and removing power from the system being monitored.

The present invention is a current imbalance detection and circuit interrupter particularly attractive for use in aircraft, for protecting a circuit having a line side and a load side. In a currently preferred embodiment, the present invention incorporates the current imbalance detection and circuit interrupter within the existing aircraft power control relay package. For example, in a fuel system application, the current imbalance detection and circuit interrupter is incorporated within the fuel pump control relay package. Therefore, the invention can be retrofit to existing aircraft, or can be utilized in newly constructed aircraft and new aircraft designs already incorporating the relay system. The current imbalance detection and fault circuit interrupter includes a housing, a power supply, a circuit to be monitored, a sensor, a logic controller, and a power controller (for example: relay, contactor, solid state relay, etc.). In a presently preferred embodiment, the invention can also include a fault indicator, a press to test switch and a reset switch. The power supply is configured to provide power to the sensor, logic controller and the power controller. The sensor is configured to sense a current imbalance in the circuit being monitored. In one presently preferred embodiment, the sensor to monitor current imbalance is a Hall effect sensor. The logic controller is configured to monitor a relay control input signal and to process inputs from the sensor.

In a presently preferred embodiment, the logic controller compares the sensor signal with predetermined limits representing acceptable operation and outputs a signal representing a circuit current imbalance when the sensor signal is outside the acceptable limits. The power controller is configured to receive input from the logic controller and remove power to the load side of the circuit when a current imbalance is sensed. In a presently preferred embodiment, the power removal from the load side of the circuit due to a sensed current imbalance is maintained until the power source to the current imbalance detection and circuit interrupter is cycled. In another presently preferred embodiment, power removal is maintained until a reset switch is activated. In a presently preferred embodiment, the fault indicator provides an indication of whether a current imbalance condition has occurred. A press to test switch may be included to check the operation of the unit during maintenance. In a presently preferred embodiment, the fault reset switch is used to reset the fault indicator.

The present invention also provides for a method for interrupting an electrical circuit for an electrical load, the electrical circuit having a line side and a load side with a ground fault. In summary, the method comprises providing a supply of power, continually monitoring and sensing the line side of the circuit for a current imbalance, continually monitoring the relay control input, receiving input from a logic controller and interrupting the relay control input signal when a current imbalance is sensed, and enabling the fault indicator. In one presently preferred aspect of the method, interrupting of the circuit when a current imbalance is sensed is maintained until the power source is cycled. Typically, the load being supplied with the current being monitored is a motor. In another preferred aspect, the current imbalance detection and circuit interrupter requires no additional signals, inputs, wiring, or sources of power, but takes its power from the circuit being monitored. In one presently preferred use of the method, the load side of the circuit is connected to a fuel pump, and arcing is terminated within the fuel pump.

In one presently preferred embodiment, the present invention is configured to perform ground fault detection and circuit interruption (GFI) and provides important advantages over prior art systems. Since the GFI system of the invention is packaged in the same envelope as an existing relay system, it can be readily retrofit to existing aircraft. Since it is easily operated off of either AC or DC circuits, containing its own power supply powered by the circuit being monitored, it can be used on either AC or DC wired aircraft without further change or rewiring in the aircraft. Furthermore, since the GFI system of the invention operates directly on and is part of the circuit being monitored, it avoids a major issue with prior art systems, which had to be separately connected to the circuit being monitored. Another substantial advantage to the present invention is that it more quickly removes power from the circuit with a fault, since sensing and control is at a single location, thus providing in situ sensing and control.

Most aircraft presently in service utilize circuit breakers with the limitations previously discussed. While the electronic and electromechanical aspects of the present invention impart additional protection to the protection provided by such circuit breakers, it would be desirable to be able to package the invention in a form which would allow ease of retrofit to existing aircraft, newly constructed and new aircraft designs, thus bringing the benefits of the invention to a wider range of applications. Accordingly, in a further presently preferred aspect of the invention, the electronic and electromechanical elements of the current imbalance detection and circuit interrupter are housed within a housing which has a similar form factor to prior art power controllers. The invention connects with the circuit to be monitored and controlled, through the existing power controller electrical connector, and it draws power from the circuit to be controlled. While there are numerous form factors which can impart additional protection to the protection provided by such circuit breakers, the most desirable form factors are related to the power controllers used in aircraft.

Other features and advantages of the present invention will become apparent from the following detailed description taken in conjunction with the accompanying drawings which illustrate, by way of example, the principles of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a block diagram of a first embodiment of a control system of the present invention adapted for a Boeing 757 aircraft, for interrupting the circuit when a current imbalance is sensed;

FIG. 2 illustrates a detailed view of the power supply portion of the control system shown in FIG. 1;

FIG. 3 illustrates a detailed view of the logic controller portion of the control system shown in FIG. 1;

FIG. 4 illustrates a detailed view of a sensor for the control system of FIG. 1;

FIG. 5 illustrates a block diagram of a second embodiment of a control system of the present invention adapted for a Boeing 747 aircraft, for interrupting the circuit when a current imbalance is sensed;

FIG. 6 illustrates a detailed view of the power supply portion of the control system shown in FIG. 5;

FIG. 7 illustrates a detailed view of the logic controller portion of the control system shown in FIG. 5;

FIG. 8 illustrates a detailed view of a sensor for the control system of FIG. 5;

FIG. 9 illustrates a block diagram of an alternate preferred embodiment of a control system of the present invention adapted for providing the speed of a DC relay in an AC application for interrupting the circuit when a current imbalance is sensed;

FIG. 10 illustrates a detailed view of a preferred embodiment of one section of the power supply portion of the control system shown in FIG. 9;

FIG. 11 illustrates a detailed view of a second section of the power supply portion of the control system shown in FIG. 9;

FIG. 12 illustrates a detailed view of the preferred logic controller portion of the control system shown in FIG. 9;

FIG. 13 illustrates a detailed view of a sensor for the control system of FIG. 9;

FIG. 14 is a side elevational view of an aircraft applicable current imbalance detection and circuit interrupter according to the present invention;

FIG. 15 is a rear view of the aircraft applicable current imbalance detection and circuit interrupter shown in FIG. 14;

FIG. 16 is a bottom view of the aircraft applicable current imbalance detection and circuit interrupter shown in FIG. 14;

FIG. 17 is a side elevational partial cutaway view of the aircraft applicable current imbalance detection and circuit interrupter shown in FIG. 14;

FIG. 18 is a sectional view of the aircraft applicable current imbalance detection and circuit interrupter taken along line 18—18 of FIG. 17; and

FIG. 19 is a sectional view of the aircraft applicable current imbalance detection and circuit interrupter taken along line 19—19 of FIG. 17.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 illustrates a preferred embodiment of a control system 10, adapted for a Boeing 757 aircraft, and FIG. 5 illustrates a preferred embodiment of a control system 10, adapted for a Boeing 747 aircraft, each being constructed in accordance with the present invention for disconnecting power to a load when a current imbalance is sensed. Referring to FIGS. 1 and 5, the aircraft applicable current imbalance detection and circuit interrupter 10 of the invention interrupts a circuit 20 having a line side 24 and a load side 26 with a ground fault. The load may be a motor, or any electrical device drawing a load, where protection of equipment or personnel is desired. The current imbalance detection and circuit interrupter of the invention includes a power supply 30, a sensor 40, a logic controller 50, a power controller 60, and a fault indicator and reset 55. The power supply is configured to provide power to the logic controller, and the sensor is configured to sense a current imbalance in the line side 20 of the circuit 24, and to output a sensor signal to the logic controller. The logic controller is configured to receive and process the sensor signal input from the sensor and the relay control input signal, and the power controller is configured to receive input from the logic controller and remove power to the load side of the circuit when a current imbalance is sensed.

FIGS. 2 and 6 illustrate a detailed view of a preferred embodiment of the power supply, and FIGS. 3 and 7 illustrate a detailed view of a preferred embodiment of the logic controller. Referring to FIGS. 4 and 8, showing a sensor for use in the control system of the invention, in a preferred embodiment of the present invention, the sensor, which is an Amploc Pro 5 Hall effect linear current sensor with an output of 233 mV/A when operated at 10V. All three line side wires pass through the sensor core. Kirchoff's current law states that the net current in a node is 0. Considering the wye connection point of the load side pump winding, the net current in the phase windings, when algebraically summed, is 0. If a ground fault exists, that is where the current is supplied through the sensor but does not return through the sensor, the algebraic sum of the currents in the phase wires would be equal to the ground fault current.

Referring to FIGS. 3 and 7, in a preferred embodiment, the output of the sensor is approximately one-half of the supply voltage, for no measured imbalance. Amplifier U3A amplifies the signal by a factor of 10. The gain is set by the ratio of resistors R5 and R3. The 3 db point is where the reactance of capacitor C4 is equal to the resistance of R5. This occurs at 3386 Hz. Resistors R1, R2, and R4 bias the amplifier and have been selected so that a maximum value of 1 meg, for resistor R4, is required to adjust the amplifier output to mid supply with the sensor at its specified worse case high output. Calibration for the worse case low output of the sensor is easily achieved.

Amplifiers U3B and U3C, and resistors R6, R7, and R8 are set to detect a current imbalance of 1.5±0.5 Arms. A high output from amplifier U3B or U3C indicates an imbalance is present in excess of the 1.5 Arms threshold. IC U4A “OR's” the outputs from amplifiers U3B and U3C. A logic 0 at its output indicates one or the other failure condition is present. Simultaneous imbalance inputs can be handled but are physically not possible since a positive imbalance cannot exist at the same time as a negative imbalance.

If a fault condition exists, it passes through IC U5A presenting a logic 1 to the latch comprised of ICs U4B and U4C. A logic 1, at pin 5, forces the output pin 4 low, turning transistor Q1 off, which removes the drive signal to the power control stage. Pin 9, the other input to the latch, is normally at logic 0. This will cause pin 10 to go high, setting the latch by presenting a logic 1 to pin 6.

In a preferred embodiment, the power-up sequence initializes the power control section to the non-operate mode. This is accomplished by presenting a logic 0 to pin 2 of IC U5A to mimic a current imbalance condition.

The power-up reset pulse created by IC U5B, resistor R13, capacitor C5 and diode CR8 is typically 7 msec. The reset is determined by the time it takes to charge capacitor C5 through resistor R13 to the threshold set by IC U5B. Diode CR8 provides a quick reset.

Referring to FIGS. 2 and 6, diodes CR1, CR2, CR3, CR4, CR5, and CR6 form a full-wave three-phase bridge. Capacitor C1 acts as the storage device for the 281V peak voltage produced by the bridge. The regulator is a preferably buck-type configuration with the abnormal architecture of having the inductor in the lower side. This is acceptable because the circuit does not have to be referenced to earth ground. In fact, the on-board electrical ground is approximately 270 V above earth ground.

Preferably, the switcher operates in a non-conventional mode. If it senses that output voltage is low, it turns on and remains on until the current through inductor L1 reaches a pre-determined amount. Otherwise, the cycle is skipped. Energy is stored in inductor L1 and transferred to output capacitor C3 through diode CR7. Proper regulation is determined by Zener VR1 and opto-coupler U2. Capacitor C2 serves to store a small amount of energy that the regulator uses to operate its internal circuitry.

Referring to FIGS. 9-13, illustrating an alternate preferred embodiment of a control system of the present invention adapted for an AC-DC application, to interrupt the circuit when a current imbalance is sensed. As is shown in FIG. 9, the aircraft applicable current imbalance detection and circuit interrupter 10 of the invention interrupts a circuit 20 having a line side 24 and a load side 26 with a ground fault. The load may be a motor, or any electrical device drawing a load, where protection of equipment or personnel is desired. The current imbalance detection and circuit interrupter of the invention includes a power supply 30, a sensor 40, a logic controller 50, a power controller 60, and a fault indication and reset 55. The power supply is configured to provide power to the logic controller, and the sensor is configured to sense a current imbalance in the line side 20 of the circuit 24, and to output a sensor signal to the logic controller. The logic controller is configured to receive the relay control input signal and to receive and process the sensor signal input from the sensor, and the power controller is configured to receive input from the logic controller and remove power to the load side of the circuit when a current imbalance is sensed.

FIGS. 10 and 11 illustrate a detailed view of a preferred embodiment of the power supply. FIG. 12 illustrates a detailed view of a preferred embodiment of the logic controller. Referring to FIG. 13, showing a sensor for use in the control system of the invention, in a preferred embodiment of the present invention, the sensor, which is an Amploc Pro 5 Hall effect linear sensor with an output of 233 mV/A when operated at 10V. All three line side wires pass through the sensor core. Kirchoff's current law states that the net current in a node is 0. Considering the wye connection point of the load side pump winding , the net current in the phase windings, when algebraically summed, is 0. If a ground fault exists, that is where the current is supplied through the sensor but does not return through the sensor, the algebraic sum of the currents in the phase wires would be equal to the ground fault current.

Referring to FIGS. 12, in a preferred embodiment, the output of the sensor is approximately one-half of the supply voltage, for no measured imbalance. Amplifier U3A amplifies the signal by a factor of 10. The gain is set by the ratio of resistors R5 and R3. The 3 db point is where the reactance of capacitor C4 is equal to the resistance of R5. This occurs at 3386 Hz. Resistors R1, R2, and R4 bias the amplifier and have been selected so that a maximum value of 1 meg, for resistor R4, is required to adjust the amplifier output to mid supply with the sensor at its specified worse case high output. Calibration for the worse case low output of the sensor is easily achieved.

Amplifiers U3B and U3C, and resistors R6, R7, and R8 are set to detect a current imbalance of 1.5±0.5 Arms. A high output from amplifier U3B or U3C indicates an imbalance is present in excess of the 1.5 Arms threshold. IC U4A “OR's” the outputs from amplifiers U3B and U3C. A logic 0 at its output indicates one or the other failure condition is present. Simultaneous imbalance inputs can be handled but are physically not possible since a positive imbalance cannot exist at the same time as a negative imbalance.

If a fault condition exists, it passes through IC U5A presenting a logic 1 to the latch comprised of ICs U4B and U4C. A logic 1, at pin 5, forces the output pin 4 low, turning transistor Q1 off, which removes the drive signal to the power control stage. Pin 9, the other input to the latch, is normally at logic 0. This will cause pin 10 to go high, setting the latch by presenting a logic 1 to pin 6.

In a preferred embodiment, the power-up sequence initializes the power control section to the non-operate mode. This is accomplished by presenting a logic 0 to pin 2 of IC U5A to mimic a current imbalance condition.

The power-up reset pulse created by IC U5B, resistor R13, capacitor C5 and diode CR8 is typically 7 msec. The reset is determined by the time it takes to charge capacitor C5 through resistor R13 to the threshold set by IC U5B. Diode CR8 provides a quick reset.

Referring to FIG. 10 and 11, diodes CR1, CR2, CR3, CR4, CR5, and CR6 form a full-wave three-phase bridge. Capacitor C1 acts as the storage device for the 281V peak voltage produced by the bridge. The regulators are a buck-type configuration with the abnormal architecture of having the inductor in the lower side. This is acceptable because the circuit does not have to be referenced to earth ground. In fact, the on-board electrical ground is approximately 270V and 260V above earth ground for the 10 V and 20V supplies respectively.

Preferably, the switcher operates in a non-conventional mode. If it is sensed that an output voltage is low, the corresponding controller turns on and remains on until the current through inductor L1 or L1A reaches a pre-determined amount. Otherwise, the cycle is skipped. Energy is stored in inductor L1 or L1A and transferred to output capacitor C3 or C3A through diode CR7 or CR7A. Proper regulation is determined by Zener VR1 or VR1A and opto-coupler U2 or U2A. Capacitor C2 or C2A serves to store a small amount of energy that each respective regulator uses to operate its internal circuitry.

Most aircraft presently in service utilize circuit breakers with the limitations previously discussed. While the electronic and electromechanical aspects of the present invention impart additional protection to the protection provided by such circuit breakers, it would be desirable to be able to package the invention in a form which would allow ease of retrofit to existing aircraft, newly constructed and new aircraft designs, thus bringing the benefits of the invention to a wider range of applications. Accordingly, in a further presently preferred aspect of the invention, the electronic and electromechanical elements of the current imbalance detection and circuit interrupter are housed within a housing which has a similar form factor to prior art power controllers. The invention connects with the circuit to be monitored and controlled through the existing power controller electrical connector, and it draws power from the circuit to be controlled. While there are numerous form factors which can impart additional protection to the protection provided by such circuit breakers, one of our form factors is related to the power controllers used in the Boeing 757 aircraft and the like, which have an installed height of approximately 1.78 inches above the mounting surface, a width of approximately 1.53 inches above the mounting surface, and a total height of 3.28 inches from the top to the bottom of the electrical terminals.

With reference to FIG. 14, in one presently preferred aspect of the invention, each of the above described circuit configurations can be advantageously contained in a corresponding housing 70, which is typically no more than about 3.28 inches (about 8.33 cm.) from top 72 to bottom 74, no more than about 1.53 inches (about 3.89 cm.) wide along its front 76 and rear 78 sides, and no more than about 2.51 inches (about 6.38 cm.) from the front side 80 of the front mounting flange 82 to the rear side 84 of the rear mounting flange 86. The housing also includes a relay 87. Referring to FIG. 14, FIG. 15, and FIG. 16, an electrical connector means such as the terminal block or connector plate 88 is provided at the bottom of the aircraft applicable current imbalance detection and circuit interrupter housing, typically with eight screw-type electrical connectors, A1, A2, X1, B1, B2, C1, C2, and X2, although other conventional types of wire connectors may also be suitable. Referring to FIG. 4, FIG. 8, FIG. 13 and FIG. 16, the connectors A1 and A2 accommodate a first line and load A; the connectors B1 and B2 accommodate a second line and load B, and the connectors C1 and C2 will accommodate a third line and load C. As is shown in FIG. 15 and FIG. 16, the connector plate is mounted to the housing of the aircraft applicable current imbalance detection and circuit interrupter by mounting screws 90, which extend through sleeves 92 in the housing, illustrated in FIG. 18 and FIG. 19, as is explained further below.

Referring to FIG. 17, FIG. 18 and FIG. 19, one or more circuit boards, such as a first printed circuit board 94 and a second printed circuit board 96, for mounting the components of the above described circuit configurations, can be mounted within the housing with notches 98 in the printed circuit boards fitting around the sleeves 92 of the mounting screws 90.

From the above, it may be seen that the present invention provides a method and apparatus for suppressing arcs in electrical equipment in aircraft which may be adapted to a variety of systems and components. As such, it provides additional reliable and rapid disconnect of power to the existing systems, thus reducing damage from ground faults in the circuits. While a particular form of the invention has been illustrated and described it will also be apparent that various modifications can be made without departing from the spirit and scope of the invention. Accordingly, it is not intended that the invention be limited except as by the appended claims. 

What is claimed is:
 1. An aircraft current imbalance detection and circuit interrupter for monitoring and interrupting an electrical power circuit to an electrical load, the electrical power circuit having a line side and a load side supplying power to an external load and a relay control signal line carrying a relay control signal used for activating a power controller used to control the flow of power to the external load, the current imbalance detection and circuit interrupter comprising: a sensor system for sensing a current imbalance in the electrical power circuit and outputting a sensor signal; an electrical power supply connected to the line side of the electrical power circuit being monitored or the relay control signal line; a logic controller powered by the power supply for outputting a fault signal representing a fault related to the sensor signal output by the sensor system in response to a current imbalance; said power controller configured to remove power to the load side of the electrical circuit responsive to the fault signal; and a housing for the sensor system, the logic controller, the power supply and the power controller, said housing being of a size and shape allowing direct replacement of an existing power controller in the aircraft and compatible with the envelope of said existing power controller, said housing including an electrical connector arrangement having equivalent electrical connections to said existing power controller.
 2. The current imbalance detection and circuit interrupter of claim 1 wherein the relay control signal line carries an AC signal.
 3. The current imbalance detection and circuit interrupter of claim 1 wherein the relay control signal line carries a DC signal.
 4. The current imbalance detection and circuit interrupter of claim 1 wherein the power controller is configured to be energized by the relay control signal.
 5. The current imbalance detection and circuit interrupter of claim 4 wherein the relay control signal comprises an AC signal and the power controller comprises an AC relay.
 6. The current imbalance detection and circuit interrupter claim 4 wherein the relay control signal comprises a DC signal and the power controller comprises a DC relay.
 7. The current imbalance detection and circuit interrupter of claim 4 wherein the relay control signal comprises an AC signal and the power controller comprises a DC relay.
 8. An aircraft current imbalance detection and circuit interrupter for interrupting an electrical circuit to an electrical load, the electrical circuit having a line side and a load side, said interrupter comprising: a housing having an envelope compatible with an existing aircraft power controller and electrical connections equivalent to electrical circuit connections of the existing aircraft power controller, said electrical circuit connections including connections for at least electrical circuit power output line connections and input electrical connections, said input electrical connections including electrical circuit power input line connections and a relay control signal input connection; at least one power supply disposed in the housing and powered by one of the input electrical connections to the current imbalance detection and current interrupter; a sensor system disposed in the housing and configured for sensing a current imbalance in the electrical circuit and for providing a sensor signal indicating the existence of a current imbalance within the electrical circuit based on said sensing of said current imbalance; a logic controller disposed in the housing and configured to be powered by said at lesat one power supply, to receive an external relay control signal from the relay control signal input connection and the sensor signal from the sensor system, and to compare the sensor signal with a predetermined range for acceptable operation for the electrical circuit and to interrupt the relay control signal when the sensor signal is outside said predetermined range; and a power controller disposed in the housing and configured to be energized by the relay control signal and to remove power to the load side of the electrical circuit when the relay control signal is interrupted.
 9. The current imbalance detection and circuit interrupter of claim 8 wherein the power supply is powered by the power input line connections.
 10. The current imbalance detection and circuit interrupter of claim 9 wherein the power input line connections interface with the electrical circuit.
 11. The current imbalance detection and circuit interrupter of claim 10 wherein the electrical circuit comprises an AC circuit.
 12. The current imbalance detection and circuit interrupter of claim 8 wherein the power supply is powered by the relay control signal input connection.
 13. The current imbalance detection and circuit interrupter of claim 12 wherein the relay control signal input connection comprises an AC signal.
 14. The current imbalance detection and circuit interrupter of claim 12 wherein the relay control signal input connection comprises a DC signal.
 15. The current imbalance detection and circuit interrupter of claim 8 wherein the power supply portion of the electrical circuit comprises three electrical lines and the sensor system comprises a single sensor associated with the electrical lines.
 16. The current imbalance detection and circuit interrupter of claim 8 wherein the external relay control signal comprises an AC signal and the power controller comprises an AC relay.
 17. The current imbalance detection and circuit interrupter of claim 8 wherein the external relay control signal comprises a DC signal and the power controller comprises a PC relay.
 18. The current imbalance detection and circuit interrupter of claim 8 wherein the external relay control signal comprises an AC signal and the power controller comprises a DC relay.
 19. The current imbalance detection and circuit interrupter of claim 8 wherein the logic controller is configured to test during a power up sequence to determine if the unit is operating properly.
 20. The current imbalance detection and circuit interrupter of claim 8 further comprising a fault indicator configured to receive said fault signal from the logic controller, and to indicate a current imbalance condition has occurred.
 21. The current imbalance detection and circuit interrupter of claim 20 further comprising a reset switch to reset the current imbalance detection and circuit interrupter after a fault has occurred. 